Many hydrocarbon wells are unable to produce at commercially viable levels without assistance in lifting the formation fluids to the earth's surface. In some instances, high fluid viscosity inhibits fluid flow to the surface. More commonly, formation pressure is inadequate to drive fluids upward in the wellbore. In the case of deeper wells, extraordinary hydrostatic head acts downwardly against the formation and inhibits the unassisted flow of production fluid to the surface.
A common approach for urging production fluids to the surface uses a mechanically actuated, positive displacement pump. Reciprocal movement of a string of sucker rods induces reciprocal movement of the pump for lifting production fluid to the surface. For example, a reciprocating rod lift system 20 of the prior art is shown in FIG. 1A to produce production fluid from a wellbore 10. As is typical, surface casing 12 hangs from the surface and has a liner casing 14 hung therefrom by a liner hanger 16. Production fluid F from the formation 19 outside the cement 18 can enter the liner 14 through perforations 15. To convey the fluid, production tubing 30 extends from a wellhead 32 downhole, and a packer 36 seals the annulus between the production tubing 30 and the liner 14. At the surface, the wellhead 32 receives production fluid and diverts it to a flow line 34.
The production fluid F may not naturally reach the surface so operators use the reciprocating rod lift system 20 to lift the fluid F. The system 20 has a surface pumping unit 22, a rod string 24, and a downhole rod pump 50. The surface pumping unit 22 reciprocates the rod string 24, and the reciprocating string 24 operates the downhole rod pump 50. The rod pump 50 has internal components attached to the rod string 24 and has external components positioned in a pump-seating nipple 31 near the producing zone and the perforations 15.
As best shown in the detail of FIG. 1B, the rod pump 50 has a barrel 60 with a plunger 80 movably disposed therein. The barrel 60 has a standing valve 70, and the plunger 80 is attached to the rod string 24 and has a traveling valve 90. For example, the traveling valve 90 is a check valve (i.e., one-way valve) having a ball 92 and seat 94. For its part, the standing 70 disposed in the barrel 60 is also a check valve having a ball 72 and seat 74.
As the surface pumping unit 22 in FIG. 1A reciprocates, the rod string 24 reciprocates in the production tubing 30 and moves the plunger 80. The plunger 80 moves the traveling valve 90 in reciprocating upstrokes and downstroke. During an upstroke, the traveling valve 90 as shown in FIG. 1B is closed (i.e., the upper ball 92 seats on upper seat 94). Movement of the closed traveling valve 90 upward reduces the static pressure within the pump chamber 62 (the volume between the standing valve 70 and the traveling valve 90 that serves as a path of fluid transfer during the pumping operation). This, in turn, causes the standing valve 70 to unseat so that the lower ball 72 lifts off the lower seat 74. Production fluid F is then drawn upward into the chamber 62.
On the following downstroke, the standing valve 70 closes as the standing ball 72 seats upon the lower seat 74. At the same time, the traveling valve 90 opens so fluids previously residing in the chamber 62 can pass through the valve 90 and into the plunger 80. Ultimately, the produced fluid F is delivered by positive displacement of the plunger 80, out passages 61 in the barrel 60. The moved fluid then moves up the wellbore 10 through the tubing 30 as shown in FIG. 1A. The upstroke and down stroke cycles are repeated, causing fluids to be lifted upward through the wellbore 10 and ultimately to the earth's surface.
The conventional rod pump 50 holds pressure during a pumping cycle by using sliding mechanical and/or hydrodynamic seals disposed between the plunger's outside diameter and the barrel's inside diameter. Sand in production fluids and during fracture flowback can damage the seals and surfaces of the plunger 80 and barrel 60. In particular, the differential pressure across the seals and surfaces causes fluid to migrate past the seals. When this migrating fluid contains sand or other solids, the seals and surfaces can become abraded by the sand so the seals eventually become less capable of holding pressure. Overtime, significant amounts of sand can collect between the plunger 80 and the barrel 60, causing the plunger 50 to become stuck within the barrel.
Production operations typically avoid using such a rod pump in wellbores having sandy fluids due to the damage that can result. However, rod pumping in sandy fluids has been a goal of producers and lift equipment suppliers for some time. To prevent sand damage, screens can be disposed downhole from the pump 50 to keep sand from entering the pump 50 altogether. Yet, in some applications, using a screen in such a location may not be feasible, and the screen and the rathole below can become fouled with sand. In other application, it may actually be desirable to produce the sand to the surface instead of keeping it out of the pump 50.
One solution to deal with sandy fluids uses extra tight seals in the pump 50 to exclude the sand. In pumping operations, however, there will always be some fluid leakage due to the pressure differential so eventually the sand will wear the seal. Extra loose hydrodynamic seals with long sealing surfaces are sometimes used to let sand pass. These long, loose hydrodynamic seals can extend the life of the pump because the longer seals can accommodate more damage than conventional rod pumps. However, damage still occurs; there is just more sacrificial surface to accept the damage. Thus, the life of the pump is extended even though damage continues.
Other solutions use features such as cups, wipers, grooved plungers, and diversion type plungers to help alleviate problems associated with sandy fluids. The cups and wipers are made from plastic, rubber, or fiber and may not be suitable in high temperature applications. Grooved plungers have radially tapered grooves that create a funnel for sand to easily find its way into.
For example, one solution to deal with sandy fluids shown in FIG. 2A uses a rod pump 50 as disclosed in U.S. Pat. No. 2,160,811. As before, the rod pump 50 has a plunger 80 disposed in a barrel 60 and has a standing valve 70 and a traveling valve 90. An upper sealing zone 84a between the plunger 80 and barrel 60 has hard metal rings 85 that engage inside the barrel 60. A lower sealing zone 84b uses the sliding cooperation between the barrel 60 and the plunger 80 to form a fluid seal. A chamber 86 is disposed between the two sealing zones 84a-b to deal with sand that may collect uphole of the plunger 80. This chamber 86 is maintained in communication with the interior 82 of the plunger 80 using circumferentially spaced ports 83.
During a downstroke of the plunger 80, the chamber 86 decreases in volume, and fluid displaces from the chamber 86 through the ports 83 and into the interior 82 of the plunger 80. Thus, any sand and silt that may have entered the chamber 86 through the upper sealing zone 84a is discharged into the plunger 80 to be removed with the main body of fluid. In this way, the sand or silt is prevented from reaching the lower sealing zone 84b and causing damage during a subsequent upstroke.
In a related solution to the rod pump 50 of FIG. 2A, a sand snare chamber can be used in the rod pump. For example, the Harbison-Fischer Sand-Pro® pump disclosed in U.S. Pat. Nos. 7,686,598 and 7,909,589 has a plunger with a sand snare chamber defined in its walls to catch the sand. (SAND-PRO is a registered trademark of Harbison-Fischer, Inc. of Crowley, Tex.) FIG. 2B shows an example of such a rod pump 50 having a sand snare chamber 100.
Again, the pump 50 has a barrel 60 with a plunger 80 located therein and has standing and traveling valves 70 and 90. The plunger 80 has a first portion 83 having a first seal 84a with the barrel 60, and the plunger 80 has a third portion 87 having a second seal 84b with the barrel 60. The first seal 84a has resilient members, while the second seal 84b is a fluid seal. An opening 81 at the top of the plunger 80 allows lifted fluid to pass up the barrel 60 and the production tubing (not shown) to be produced.
In between the first and second portions 83 and 87, the plunger 60 has a second portion 85 that forms a balancing chamber 86 between the barrel 60 and the plunger 80. The plunger's second portion 85 also has an opening 88 to allow communication between the plunger's interior 82 and the balancing chamber 86. A wall 89 is located relative to the opening 88 and forms a sand snare chamber 100 between the balancing chamber 86 and the plunger interior passage 82.
To pump fluid from a sandy well, the plunger 80 reciprocates with respect to the barrel 60. Pressure equalizes across the first seals 84a by venting pressure from inside of the plunger 82 to outside of the plunger 80 in the balancing chamber 86 between the two seals 84a-b. In the meantime, the pump 50 uses the wall 89 to capture sand from the fluid exiting the opening 88 in the sand snare chamber 100. This collection isolates the sand from the sets of seals 84a-b to reduce wear.
Unfortunately, the sand snare chamber 100 on the pump 50 has some drawbacks. For example, the volume available to collect sand can be limited. In addition, the chamber 100 can create turbulence during pumping which can tend to keep the sand flushed out of the sand snare chamber 100 and into the sealing areas 84a-b. 
Yet another solution of a downhole pump for use in sandy fluids is disclosed in U.S. Pat. No. 8,858,187 to Lane.
In another solution briefly mentioned above, a diversion plunger can be used in a rod pump to deal with sandy fluid. FIG. 3A illustrates a typical downhole pump according to the art having a form of diversion plunger. A traveling assembly 150 includes a valve-rod bushing 152, a rod 154, a top connector 156, a plunger 158, a cage 160, a ball valve 162, and a seat 164. A seating assembly includes a cup assembly 112 and a bushing 114, which connects to a stationary assembly having a barrel 116, a cage 118, a ball valve and seat 120, and a barrel-cage bushing 122.
For use, the traveling assembly 150 is disposed in the seating and stationary assembly 110 and can reciprocate therein with a rod string connected to the valve-rod bushing 152. The rod 154 extends out of the cup assembly 112, and the plunger 158 with its top connector 156, cage 160, ball valve 162, and seat 164 is movably disposed inside the barrel 116. The barrel 116 disposes in production tubing with a pump seating nipple or other component as conventionally done, and the pump can be used to lift production fluids of a well to the surface as the plunger 158 reciprocates in the barrel 116.
The barrel 116 defines an interior in which the plunger 158 is disposed, and the plunger 158 defines an interior as well. The standing valve 120 permits fluid flow from the production tubing (not shown) to flow into the barrel's interior, but restricts fluid flow in the opposite direction. The traveling valve 162 permits fluid flow from the barrel's interior (and especially a variable volume between the valves 162 and 120) to enter the plunger's interior, but restricts fluid flow in the opposite direction.
A gap is formed between the plunger 158 and the barrel 116, and a fluid or hydrodynamic seal that uses the fluid trapped in the gap can hold pressure. As noted above, the hydrodynamic seal can be formed by long sealing surfaces along the plunger 158 and the barrel 116, which can help deal with sandy fluids. Additionally, the outside surface of the plunger 158 can be hardened with a coating or the like to increase resistance to wear. Typically, the inside surface of the barrel 116 and the outside surface of the plunger 158 have a tight clearance to create the fluid seal. The actual clearance can depend in part on the type of fluid to be encountered, such as heavy or light crude, expected particulate sizes, and other details of the pump.
In the rod pumping application, sand can migrate between the barrel 116 and the plunger 158 and can cause damage/scoring to the plunger 158 and/or barrel 116, which eventually leads to poor pumping efficiency and pump failure. To help mitigate damage, the pump 50 can use features of the top connector 156 for the plunger 158. As shown, the top connector 156 is threaded onto the upper end of the plunger 158. The top connector 156 not only connects to the rod 154, but reciprocates with the plunger 158 in the barrel 116 and provides outlets 157 for lifted fluid from the interior 159 of the plunger 158.
FIG. 3B shows an example of a current top connector 200 for a diversion plunger. The top connector 200 includes a body 210 with a flow passage 212 therethrough. A threaded end 214 of the flow passage 212 threads onto an uphole end of the plunger 158, and outlet openings 213 of the passage 212 communicate the plunger's interior 159 out the upper end of the connector 200. The top end 216 of the connector body 210 is also threaded to connect to a rod (e.g., 154: FIG. 3A). The connector body 210 has an edge 218 that is used in mitigating passage of sand past the connector body 210 toward the outside surface of the plunger 158.
The threaded connection 214 creates a concentricity issue between the plunger 158 and the connector body 210 and must be machined to a very close tolerance. In fact, to mitigate the travel of sand past the body 210 and its sharp edge 218, the outside surface of the connector body 210 is machined to the diameter of the plunger 158. For this reason, axial alignment of the connector 200 with the plunger 158 is crucial due to 0.002-0.005-in. typical barrel clearance typically used for downhole pumps. Additionally, the connector 200 must be made of a tough, hard material to withstand the operational depths and to resist sand scoring and corrosion. Thus, the connector 200 is restricted to particular types of materials/coatings that can be used because the components must meet particular operational constraints of hardness/toughness for the application.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.